              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460
              OFFICE OF CHEMICAL SAFETY
AND POLLUTION PREVENTION
                 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
                            WASHINGTON, D.C.  20460







                                                                PC Code: 128847
                                                             DP Barcode: 421092
                                                                               
                                                        Date: November 13, 2014
                                                                               
                                                                               
                                                                    MEMORANDUM	

SUBJECT:	Drinking Water Exposure Assessment in support of the new use registration of multiple difenoconazole formulated products  on Artichoke, Berry Bushberry Subgroup 13-07B, Ginseng,  and Bean and Pea, Dried Shelled (except Soybean) Subgroup 6C as well as Conversion of Stone Fruit Crop Group 12-12 and  Tree Nuts Crop Group 14-12. 

TO:	Laura Nollen, Risk Manager Reviewer
	Barbara Madden, Risk Manager
	Marion Johnson, Branch Chief
               Registration Division (7505P)
               
               Thurston Morton, Chemist
	Elissa Reaves, Branch Chief
               Risk Assessment Branch IV
               Health Effects Division (7509P)
	
FROM:	Faruque Khan, Ph.D., Senior Fate Scientist
	Environmental Risk Branch I
	Environmental Fate and Effects Division (7507P)

APPROVED
 BY:	Sujatha Sankula, Ph.D., Branch Chief, 	
               Environmental Risk Branch I	
	Environmental Fate and Effects Division (7507P)

	This assessment provides estimated drinking water concentrations (EDWCs) of difenoconazole and its major metabolite, CGA-205375 (M1) in surface water and groundwater in support of human health risk assessment on the Interregional Research Project Number 4 (IR4) proposed new uses on ginseng, artichoke, and conversion on stone fruit group 12-12 and tree nut group 14-12. The Residues of Concern Knowledgebase Subcommittee (ROCKS) of the Health Effects Division (HED) recommended to include CGA-205375 as a residue of concern for drinking water (USEPA, 2011, DP 391350). Therefore, this drinking water assessment was performed using total toxic residue (TTR; i.e. parent plus CGA 205375) method in support of the proposed Section 3 new uses following the approach used in a previous drinking water assessment for canola (US EPA 2013a, DP412614). Foliar spray applications (both aerial and ground spray applications) and chemigation, are being proposed for these crops.  The EDWCs of difenoconazole and its major metabolite, CGA-205375 (M1) were generated using application rates of 0.46 to 0.52 lbs a.i./A.with the Surface Water Concentration Calculator model for surface water as well as the maximum application rate of 0.52 lbs a.i./A with the PRZM-GW and SCI-GROW models for groundwater. 

	The Interregional Research Project Number 4 (IR-4) also revised the existing crop groupings by converting stone fruit Group 12 to stone fruit Group 12-12 and nut tree Group 12 to nut tree Group 14-12. Since there are no changes in the application rates and methods for the revised crop groupings, previous drinking water assessments (stone fruit; USEPA, 2010; DP426124 and tree nut; USEPA 2009, DP340378) fulfill the requirement for refining EDWCs for these crops. EFED noticed that the application rate for cucurbit is higher in the submitted Inspire Super (EPA Reg. No. 100-1317) label as compared to previous label, which was stamped on August 03, 2012. Since the maximum applicant rate of 0.52 lbs a.i./A for cucurbit is higher than previously assessed application rate of 0.46 lbs a.i./A (USEPA 2009; DP361398 the EDWCs for the revised rate of cucurbit was  reassessed. 

      Surface water and groundwater modeling were conducted for the maximum annual application rate of 0.46 to 0.52 lbs a.i./A  for aerial application only as aerial applications produce conservative estimates. Remaining model input parameters were chosen according to current guidance (USEPA, 2009 and USEPA, 2013b). For surface water, the EDWCs for new uses and the revised application rate for cucurbit did not exceed the recommended peak (acute) concentration of 20.0 ug/L, annual mean (non-cancer chronic) concentration of 13.6 ug/L and the 30 year annual average concentration (cancer chronic) of 9.9 ug/L reported in the previous drinking water assessment based on grape use (US EPA, 2013; DP 398836). Recently, PRGM-GW scenarios were revised and consequently the estimated PZRM-GW groundwater concentrations were reduced to 1.77 ug/L from 2.24 ug/L and chronic concentration of 0.66 ug/L from 0.78 ug/L for the maximum application rate for FL citrus scenario. Recommended surface water and groundwater EDWCs for human health are listed in Table 1. 
      
Table 1.  Tier II Drinking Water Exposure Estimates for Total Toxic Residues of Difenoconazole Use on Canola/Oilseed Subgroup 20A.
Source
Peak Exposure (μg/L)
Annual Mean Exposure (μg/L) 
30-year Average Exposure (ug/L)
Surface water[1]
20.0
13.6
9.9
Groundwater[2]
1.77
---
0.66
[1] EDWCs generated using PRZM/EXAMS model for aerial application of 0.46 lbs a.i./A for grape use (USEPA 2013)
2 Groundwater EDWCs are based on PRZM-GW 100 years simulation and the highest application rate for difenoconazole

      
      Drinking Water Exposure Modeling
Models

	The EDWCs were generated using EFED's standard suite of models.  Since there is no modification of input parameters for SWCC (same as  PRZM/EXAMS, PRZM-GW and SCIGROW models, detailed description of models and inputs parameters can be obtained from the previous assessment (USEPA, 2013, D412416). However, inputs for SWCC in Table A-1, for SCIGROW in Table A-2 , for PRZM-GW in Table A-3 as well as sample outputs of SWCC, PRZM-GW and SCIGROW models were provided in the Appendix A. Information concerning the model can be found on the EPA Water Models web-page  (USEPA, 2010b)	

	Surface Water

 	The Surface Water Concentration Calculator (SWCC v 1.106) model was used to generate EDWCs for the Tier II aquatic exposure assessment. The SWCC is a graphical user interface that runs the Pesticide Root Zone Model (PRZM, v 5, November 15, 2006) and the Variable Volume Water Body Model (VVWM, 3/6/2014) (USEPA, 2006b). Simulations are run for multiple (usually 30) years and the EDWCs represent peak values that are expected once every ten years based on the thirty years of daily values generated during the simulation. The default PCA of 1.0 was used for the proposed uses because difenoconazole can be used in both agricultural and non-agricultural settings (USEPA 2012). Estimated difenoconazole concentrations in surface water used for drinking water are summarized in Table 2. The EDWCs for surface water for new uses and cucurbit did not supersede the previously recommended drinking water concentrations based on canola use (Table 1).

Table 2.  EDWCs Based on Total Toxic Residues of Difenoconazole for Proposed New Uses 
Drinking Water Source
Crop 
Crop Scenario
                             Peak (Acute) Exposure
                                       
                             Annual Mean (chronic)
                                   Exposure 
                    30-year Mean (cancer chronic) Exposure



             -----------------------(μg/L)-----------------------
Surface Water[1]
Artichoke
CArowcropRLF
                                     6.54
                                     5.28
                                     3.97

Ginseng
MNsugarbeetSTD
                                     7.48
                                     5.50
                                     4.19

Bushberry
NYgrapesSTD
                                     15.0
                                     10.4
                                     7.52


ORberriesOP
                                     7.58
                                     5.61
                                     4.54

Legumes
MIbeanSTD
                                     8.89
                                     5.38
                                     3.96


WAbeanNMC
                                     9.52
                                     6.97
                                     4.95

Cucurbit
FLcucumberSTD
                                     8.81
                                     3.66
                                     2.74


CAmelonRLF
                                     8.13
                                     5.57
                                     4.50
Ground water
FL Citrus  Scenario[2]
                                     1.77
                                      ---
                                     0.66

Generic Scenario[3]
                                   1.48E-02
                                      ---
                                   1.48E-02
[1] EDWCs generated using SWCC model for aerial application 
[2] Highest EDWCs generated using PRZM-GW model based on 0.52 lbs a.i/A for cucurbit for the highest exposure observed in the previous drinking water assessment (USEPA, 2013)
[3] EDWCs generated using SCIGROW model and assumed 5 equal application rate of 0.114 lbs a.i./A for cucurbit
      
      Groundwater 

The Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003) model[1] is a regression model used as a screening tool to estimate pesticide concentrations found in groundwater that is used for drinking water. SCI-GROW was developed by fitting a linear model to ground water concentrations with the Relative Index of Leaching Potential (RILP) as the independent variable.  Ground water concentrations were taken from 90-day average high concentrations from Prospective Ground Water studies. PCAs are not applicable for the SCI-GROW model.

In addition, Tier 1 groundwater EDWCs for difenoconazole, resulting from its use on cucurbit for its higher application rate of 0.52 lbs a.i./A was also estimated using the PRZM-GW model (USEPA, 2012c), with the GW-GUI (Graphical User Interface, version 1.0, August 31, 2012).  PRZM-GW is a one-dimensional, finite-difference model that estimates the concentrations of pesticides in groundwater.  It accounts for pesticide fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field.  PRZM-GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site. PRZM-GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rural agricultural field following many years of pesticide application. 
Recently, PRGM-GW scenarios were revised and consequently the estimated PZRM-GW groundwater concentrations were reduced to 1.77 ug/L from 2.24 ug/L and chronic concentration of 0.66 ug/L from 0.78 ug/L for the maximum application rate for FL citrus scenario reported in previous drinking water assessment (USEPA, 2013, DP412416). The EDWCs for groundwater for new uses and cucurbit (Table 2) superseded the previously recommended drinking water concentrations (Table 1).
      
      Monitoring Data
      
Monitoring data for difenoconazole were available from the United States Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program Data Warehouse, searched on November 06, 2014.  Difenoconazole was detected in only one of seventy two surface water samples from multiple states (CA, GA, IA, IN, MO, NE and WI); the reported maximum concentration (18.2 ng/L) was detected in California.  Difenoconazole was not detected at the limits of quantitation (LOQ) of 0.6 and 1.0 ug/kg-sediment in any of the 83 sediment samples collected from multiple states (GA, IA, IN, KS, KY, MO, NE, OH, SD and WI).  However, the study design of NAWQA is not targeted to account for all difenoconazole use areas; timing of application and other factors which may more accurately represent spatially and temporally dependent variables influencing runoff vulnerability. No groundwater data are available at this time.

Monitoring data for surface water, groundwater, and sediment from the California Department of Pesticide Regulation (CDPR) were searched on November 06, 2014.  No monitoring data were available for difenoconazole on CDPR's website.



                                  References


US EPA, 2009a.  Difenoconazole Drinking Water Assessment in Support of New Use Registration Action for Bulb Vegetables, Brassica (Cole) Leafy Vegetables, Cucurbit Vegetables, Citrus Fruit, Grapes, and Tree Nuts.  May 28, 2009. (D361398) 

USEPA.  2009b. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version 2.1.  U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects Division, October 22, 2009. 

USEPA. 2010. Drinking Water Exposure Assessment to Establish a Tolerance of parent
 	difenoconazole on carrot, chickpeas, soybean, stone fruits, and strawberry. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency (D426124).
USEPA.  2011.  Difenoconazole:  Report of the Residues of Concern Knowledgebase Sub-committee (ROCKS). Health Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency (D391350) 

 US EPA. 2012c. Memorandum: Approval of PRZM-GW for use of Drinking Water Exposure Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.
 
 USEPA 2013a. Drinking Water Exposure Assessment in support of the new use registration of difenoconazole formulated product Inspire on Canola/Oilseed Subgroup 20A. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency (D 412614).
 
 USEPA, 2013b. Guidance on modeling off-site deposition of pesticides via spray drift for ecological and drinking water assessments. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency
 

                                  APPENDIX A
                                       
                                       

The input parameters used for SWCC modeling.

Table A-1. Chemical Specific SWCC Model Input Parameters for Difenoconazole

                                   Parameter
                             Input Value and Unit
                                Source/Comments
Crops 
Artichoke
Ginseng
Bushberry
Legumes
Cucurbit

Scenario
CArowcrop RLF
MNsugarbeetSTD
ORberriesOP and NYgrapeSTD
MIbeanSTD and WAbeanNMC
FLcucumberSTD an CAMelonRLF


Surrogate scenario
Surrogate scenario
Surrogate scenarios
Standard and surrogate scenarios
Standard and surrogate scenarios

Maximum single application rate x Maximum # of application

Artichoke, ginseng, bushberry, and legumes 



Cucurbit 





0.115 lbs a.i./A (0.129 kg a.i/HA) x 4




0.114 lbs a.i./A (0.128 kg a.i./HA) x 4 and 0.064 lbs a.i./A (0.072 kg a.i./HA) x 1





EPA Reg. No. 100-1262,
EPA Reg. No. 100-1312
EPA Reg. No. 100-1313 
EPA Reg. No. 100-1317

EPA Reg. 100-1317
Method of application
CAM = 2

Foliar Spray 


Product Label as above
Application efficiency 
0.95 (Aerial Spray)

Generally aerial scenario generates higher exposure as compared to ground and chemigation scenarios 

EFED Model Input Guidance, Version 2.1 (2009b) a
Spray drift
0.135 (Aerial Spray)
USEPA 2013. 
Crop
Scenario: Application date and minimum interval between applications (days)
Artichoke
   CArowcrop: June 9 (14)
Assumed 21-days for application intervals between 2[nd] and 3[rd]

Ginseng
    MNsugarbeet: Sept 17 (7)
Assumed 14-days for application intervals between 2[nd] and 3[rd]

Busherry
  ORberries: June 19 (7)
   NYgrape: Sept 10 (7)
Assumed 14-days for application intervals between 2[nd] and 3[rd]

Legume
    MIbean:July 03
     WAbeanOP: July 01
Assumed 14-days for application intervals between 2[nd] and 3[rd]

Cucurbit
    FLcucumber: Oct 22 (7)
    CAmelon: June 14 (7)
Assumed 14-days for application intervals between 2[nd] and 3[rd] and 4[th] and 5[th]
Hydrolysis
Stable
MRID 42245127
Aerobic soil metabolism (t1/2)[b]
489.6 days
MRIDs: 42245131, 46950109-12, and 46950114
Aerobic aquatic metabolism (t1/2) c
632.9 days
MRIDs: 46950116 & 46950117
Anaerobic aquatic metabolism (t1/2) d
1485.3 days
MRID 46950119
Aquatic photolysis t1/2 (days) e
Stable
MRID 46950105
Vapor pressure
2.5 x 10-10 mm Hg (25 [o]C)
MRID 46515901
Solubility in water 
15 mg/L (25 [o]C)
MRID 46515901
Molecular Weight
406.27 
MRID 46950104
Partition coefficient Koc
5381 mL/g
MRIDs: 42245135 and 46950121
[a] Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides (Version 2.1; Oct. 22, 2009)
[b] The 90% of the UCL of the mean metabolism Half-life.
[c] The 90% of the UCL of the mean metabolism Half-life of all available Half-lives but those obtained for high test rate.
[d] Half-life was multiplied by three (i.e., 3 x 495.1 days).
[e] Estimated Half-life is beyond the duration of study, thus considered stable.

Sample Output:
Summary of Water Modeling of Difenoconazole and the USEPA Standard Reservoir
Estimated Environmental Concentrations for Difenoconazole are presented in Table 1 for the USEPA standard reservoir with the NYGrapesSTD field scenario. A graphical presentation of the year-to-year peaks is presented in Figure 1. These values were generated with the Surface Water Concentration Calculator (SWCC Version 1.106). Critical input values for the model are summarized in Tables 2 and 3.
This model estimates that about 2.3% of Difenoconazole applied to the field eventually reaches the water body. The main mechanism of transport from the field to the water body is by erosion ( 68% of the total transport), followed by spray drift (17.6%) and runoff (14.5%).
In the water body, pesticide dissipates with an effective water column half-life of 199.7 days. (This value does not include dissipation by transport to the benthic region; it includes only processes that result in removal of pesticide from the complete system.) The main source of dissipation in the water column is washout (effective average half-life = 228.7 days) followed by metabolism (1579.9 days) and volatilization (3.965328E+07 days).
In the benthic region, pesticide dissipation is negligible (3702.7 days). The main source of dissipation in the benthic region is metabolism (effective average half-life = 3702.7 days). The vast majority of the pesticide in the benthic region (99.83%) is sorbed to sediment rather than in the pore water.
Table 1. Estimated Environmental Concentrations (ppb) for Difenoconazole.
Peak (1-in-10 yr)
15.0
4-day Avg (1-in-10 yr)
14.2
21-day Avg (1-in-10 yr)
12.6
60-day Avg (1-in-10 yr)
11.6
365-day Avg (1-in-10 yr)
10.4
Entire Simulation Mean
7.52

Table 2. Summary of Model Inputs for Difenoconazole.
Scenario
NYGrapesSTD
Cropped Area Fraction
1.0
Koc (ml/g)
5381
Water Half-Life (days) @ 25 °C
632.9
Benthic Half-Life (days) @ 25 °C
1483.3
Photolysis Half-Life (days) @ 40 °Lat
0
Hydrolysis Half-Life (days)
0
Soil Half-Life (days) @ 25 °C
489.6
Foliar Half-Life (days)

Molecular Wt
406.27
Vapor Pressure (torr)
2.5E-10
Solubility (mg/l)
15

Table 3. Application Schedule for Difenoconazole.
Date (Mon/Day)
Type
Amount (kg/ha)
Eff.
Drift
09/10
Foliar
0.129
0.95
0.135
09/17
Foliar
0.129
0.95
0.135
10/01
Foliar
0.129
0.95
0.135
10/08
Foliar
0.129
0.95
0.135

Figure 1. Yearly Peak Concentrations





                      Input and Output of SCI-GROW Model

The input parameters used for SCI-GROW modeling

Table A-2. SCI-GROW Input Parameters for Difenoconazole Applied on Multiple Crops at the Maximum Label Application Rate.
Model Input Variable
Input Values
Koc (the lowest value of all available Kocs, MRIDs: 42245135 and 46950121)[1]
3471 ml/g
Application Rate
 0.114lb. a.i./acre 
Number of Applications 
5
Aerobic Soil Metabolism half-life[2]
223.6 days
Hydrolysis
Stable
[1] The Koc shows greater than three-folds variation, thus, the lowest value was uses per guidance as of Oct. 22, 2009 (USEPA 2009b).
[2] Median of seven values.
                                       
                                       
                          Output of  SCIGROW modeling
                                       
                                    SCIGROW
                                               VERSION 2.3
                          ENVIRONMENTAL FATE AND EFFECTS DIVISION
                                  OFFICE OF PESTICIDE PROGRAMS
                            U.S. ENVIRONMENTAL PROTECTION AGENCY
                                            SCREENING MODEL
                                FOR AQUATIC PESTICIDE EXPOSURE
                                        
                              SciGrow version 2.3
                            chemical:Difenoconazole
                          time is 10/27/2014  16:32:17
    ------------------------------------------------------------------------
       Application      Number of       Total Use    Koc      Soil Aerobic
     rate (lb/acre)  applications   (lb/acre/yr)  (ml/g)   metabolism (days)
    ------------------------------------------------------------------------
            0.114           5.0           0.570      3.47E+03      223.6
    ------------------------------------------------------------------------
                 groundwater screening cond (ppb) =   1.48E-02 
    ************************************************************************
                                       
                                       

                     Input and Output of  PRZM-GW modeling
                                       
                                       
Table A-3. PRZM-GWInput Parameters[1] for Difenoconazole Uses  
                                       
                                 Variable Name
                                       
                                  Data Value
                                  Data Source
                                    MRID(s)
                                    Comment
Application Method
Aerial (Cucurbit)

Proposed labels
                               EPA Reg# 100-1317
                                       
Maximum Single Application Rate X Maximum # of application
(lbs. a.i./acre) [kg/ha]
Cucurbit
0.114 [0.128] x 4 plus 
0.064 (0.072) x 1
Proposed labels
                               EPA Reg# 100-1317
                                       
Application Interval (days)
7 
Proposed labels
                               EPA Reg# 100-1317
                                       
Hydrolysis, DT50 (Days)
stable
MRID 42245127
                                      ---
Aerobic Soil Metabolism  DT50 (Days) 
489.6 days
MRIDs.: 46950116 & 46950117
The 90% of the upper confidence limit (UCL) of the mean metabolism half-life.
                                       
Koc (mL/goc)
5381
MRIDs: 42245135 and 46950121
Average Koc
[1] EFED input parameter guidance: http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.htm


                                       

Groundwater Analysis for Difenoconazole and the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario
Estimated groundwater concentrations and breakthrough times for Difenoconazole are presented in Table 1 for the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.dvf) - Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values were generated with the PRZM-GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Difenoconazole and the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.dvf) - Astatula sand, hrgb A Scenario.
Peak Concentration (ppb)
    1.78
Post-Breakthrough Mean Concentration (ppb)
Incomplete
Entire Simulation Mean Concentration (ppb)
   0.659
Average Breakthrough Time (days)
Incomplete
Throughputs
0.8163512

Table 2. Chemical Properties for Groundwater Modeling of Difenoconazole.
Koc (ml/g)
5381
Surface Soil Half Life (days)
490
Hydrolysis Half Life (days)
0
Diffusion Coefficint Air (cm2/day)
0
Henry's Constant
0.0
Enthalpy (kcal/mol)
0.0

Table 3. Pesticide application scheme used for Difenoconazole.  This application scheme was applied every year of the simulation.
Application Date
(Month/Day)
Application Method
Application Rate
(kg/ha)
10/22
Ground application with mass distribution increasing proportionally with depth to 4 cm
0.128
10/29
Ground application with mass distribution increasing proportionally with depth to 4 cm
0.128
11/12
Ground application with mass distribution increasing proportionally with depth to 4 cm
0.128
11/19
Ground application with mass distribution increasing proportionally with depth to 4 cm
0.128
12/03
Ground application with mass distribution increasing proportionally with depth to 4 cm
0.072

Figure 1. Aquifer Breakthrough Curve for Difenoconazole and the Florida Citrus - FL Central Ridge, Polk County - (Tampa) Met File (12842.Dvf) - Astatula Sand, Hrgb A Scenario

                                       
